U.S. patent number 3,819,256 [Application Number 05/279,869] was granted by the patent office on 1974-06-25 for apparatus for refracting the eye.
This patent grant is currently assigned to SAID Bellows, by said Borough. Invention is credited to John G. Bellows, Howard C. Borough.
United States Patent |
3,819,256 |
Bellows , et al. |
June 25, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
APPARATUS FOR REFRACTING THE EYE
Abstract
An apparatus for refracting the eye utilizes two separate
optical paths to minimize stray light and optical interference. The
apparatus includes dual lens means, each disposed along one of the
optical paths, for selectively varying the spatial relationship of
a beam of radiant energy passing therethrough. The apparatus
comprises a source of radiant energy, modulating means for forming
a modulated beam of radiant energy, first lens means, projecting
means for introducing a portion of the beam into the eye and for
receiving and projecting a reflection of the beam from the retina
of the eye along the second optical path, second lens means coupled
to the first lens means, and analysis means for forming an image of
the reflection and determining the sharpness of focus of the image.
The modulating means comprises a dual bladed light chopper which
presents to the eye an image of a moving slit representing in
alternate succession two apparent sources of radiant energy at two
spaced apart distances. The lens means are automatically adjusted
to achieve optimum sharpness of focus and the magnitude of the
correction to the lens means corresponds to the refractive
correction required by the eye. Image rotation prisms are disposed
along each of the optical paths and together with the analysis
means through suitable electronic coupling provide an indication of
the presence and magnitude of an astigmatic condition of the
eye.
Inventors: |
Bellows; John G. (Chicago,
IL), Borough; Howard C. (Seattle, WA) |
Assignee: |
SAID Bellows, by said Borough
(N/A)
|
Family
ID: |
23070704 |
Appl.
No.: |
05/279,869 |
Filed: |
August 11, 1972 |
Current U.S.
Class: |
351/211; 351/205;
356/126; 250/200; 351/214; 356/128 |
Current CPC
Class: |
A61B
3/103 (20130101) |
Current International
Class: |
A61B
3/103 (20060101); A61b 003/00 (); G01n
021/46 () |
Field of
Search: |
;351/6,13,14,15,16
;356/126,128 ;250/200 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J Warshawsky, JOSA, Vol. 54, No. 3, 3-1964, pp. 375-379. .
F. W. Campbell et al., JOSA, Vol. 49, No. 3, 3-1959, pp. 268-272.
.
The Optician, Vol. 152, No. 3943, 10-28-1966, pp. 433-434. .
Amer. J. Optom. & Arch. Amer. Acad. Optom., Vol. 37, 1960, pp.
403-407. .
J. Optom. & Arch. Amer. Acad. Optom., Vol. 39, July 1962, pp.
356-361..
|
Primary Examiner: Corbin; John K.
Assistant Examiner: Sacher; Paul A.
Attorney, Agent or Firm: Arnstein, Gluck, Weitzenfeld &
Minow
Claims
We claim:
1. An apparatus for testing the eye comprising
a. a source for generating radiant energy;
b. modulating means aligned with said source along a first optical
path for modulating a portion of the radiant energy generated by
said source into a beam,
c. first lens means aligned along said first optical path for
selectively varying the spatial relationship of said beam of
radiant energy,
d. projection means aligned along said first optical path for
introducing into the eye at least a portion of said beam of radiant
energy from said first lens means and for receiving and projecting
along a second optical path at least a portion of a beam of radiant
energy reflected from the retina of the eye upon introduction of
said portion of said first beam into the eye;
e. second lens means aligned along said second optical path and
being coupled with said first lens means for varying the spatial
relationship of said reflected portion from said projection means
with said first lens means; and
f. analysis means for forming an image of said portion of the beam
of radiant energy reflected from the retina of the eye and for
determining the sharpness of focus of said image.
2. The apparatus as defined in claim 1 wherein said analysis means
includes means responsive to the sharpness of focus of said image
for controlling said first and second lens means to achieve optimum
sharpness of focus of the image.
3. The apparatus as defined in claim 2 wherein said analysis means
comprises
a. target means aligned along said second optical path for
translating at least a part of said portion of the beam of radiant
energy reflected from the retina of the eye into focused modulated
pulses of radiant energy;
b. radiant energy detecting means responsive to said modulated
pulses of radiant energy to receive said pulses and transmit a
signal which is modulated in accordance with the sharpness of focus
of said modulated pulses of radiant energy, and
c. control means responsive to said signal which is modulated in
accordance with the said sharpness of focus for controlling said
first and second lens means to achieve optimum sharpness of focus
of the said modulated pulses of radiant energy at said target
means.
4. The apparatus as defined in claim 1 wherein said modulating
means includes means for modulating said portion for presenting to
the eye an image of a moving slit representing in alternating
succession two apparent sources of radiant energy at two spaced
apart distances.
5. The apparatus as defined in claim 4 wherein said analysis means
includes means responsive to the sharpness of focus of said image
in conjunction with said modulating means for controlling said
first and second lens means to achieve optimum sharpness of focus
of said image.
6. The apparatus as defined in claim 1 wherein said first lens
means and said second lens means each comprise a lens system of
independently variable spherical power, cylindrical power, and
cylinder axis orientation.
7. The apparatus as defined in claim 6 wherein said modulating
means includes means for modulating said portion for presenting to
the eye an image of a moving slit representing in alternating
succession two apparent sources of radiant energy at two spaced
apart distances, and wherein said analysis means includes spherical
power control means responsive to said sharpness of focus of said
image in conjunction with said modulating means for controlling
said variable spherical power of said first and second lens means
to achieve optimum sharpness of focus.
8. The apparatus as defined in claim 1 including first image
rotation means interposed and aligned along said first optical path
for rotating said beam of radiant energy about the axis of said
first optical path in a first direction, and second image rotation
means interposed and aligned along said second optical path for
rotating said reflected portion about the axis of said second
optical path in a direction opposite to said first direction, said
second image rotation means being coupled to said first image
rotation means to rotate therewith at the same rotational speed,
and said first and second image rotation means in conjunction with
said analysis means providing indication of the presence and
magnitude of astigmatism of the eye.
9. An apparatus for testing the eye comprising
a. source means for generatng radiant energy;
b. modulating means aligned with said source means along a first
optical path for modulating a portion of the radiant energy
generated by said source means into a beam for presenting to the
eye an image of a moving slit representing in alternate succession
two apparent sources of radiant energy at two spaced apart
distances;
c. first image rotating means alinged along said first optical path
for rotating said beam of radiant energy modulated by said
modulating means about the axis of said first optical path in a
direction; directon;
d. first lens means aligned along said first optical path for
selectively varying the spatial relationship of said beam of
radiant energy from said first image rotation means comprising a
lens system of independently variable spherical power, cylindrical
power, and cylinder axis orientation;
e. projection means aligned along said first optical path for
introducing into the eye at least a portion of said beam of radiant
energy from said first lens means and for receiving and projecting
along a second optical path at least a portion of a beam of radiant
energy reflected from the retina of the eye upon introduction of
said first beam into the eye;
f. second lens means aligned along said second optical path and
being coupled with said first lens means for varying the spatial
relationship of said reflected portion from said projection means
with said first lens means, said second lens means comprising
independently variable spherical power, cylindrical power and
cylinder axis orientation;
g. second image rotation means aligned along said second optical
path for rotating said reflected portion from said second lens
means about the axis of said second optical path in a direction
opposite to said first direction, said second image rotation means
being coupled to said first image rotation means to rotate
therewith at the same rotational speed; and
h. analysis means for analyzing the spatial relationship of said
reflected portion from said second rotation means comprising
1. target means aligned along said second optical path for
translating at least a part of said reflected portion into focused
modulated pulses of radiant energy,
2. radiant energy detecting means responsive to said modulated
pulses of radiant energy for analyzing the sharpness of focus
thereof,
3. spherical power control means responsive to said sharpness of
focus in conjunction with said modulating means for controlling
said variable spherical power of said first and second lens means
to achieve optimum sharpness of focus, and
4. cylindrical power control means responsive to said sharpness of
focus in conjunction with the rotation of said first and second
image rotation means for controlling said variable cylindrical
power and cylinder axis orientation of said first and second lens
means to achieve optimum sharpness of focus.
10. The apparatus of claim 9 wherein said radiant energy detecting
means includes means to receive said modulated pulses of radiant
energy and transmit a signal which is modulated in accordance with
the sharpness of focus of said modulated pulses of radiant energy,
said spherical power control means being operable to control said
variable spherical power of said first and second lens means to
achieve optimum sharpness of focus in accordance with said signal
in conjunction with said modulating means, and said cylindrical
power control means being operable to control said cylindrical
power and cylinder axis orientation of said first and second lens
means to achieve optimum sharpness of focus in accordance with said
signal in conjunction with the rotation of said first and second
image rotation means.
Description
BACKGROUND OF THE INVENTION
This invention relates to an apparatus for objectively and
automatically refracting the eye.
While the invention will be described in terms of its application
to the testing and refractive correction of the human eye, it will
be understood that it has application in the collimation or
calibration of other optical systems.
Apparatus for objectively and automatically refracting the eye is
disclosed in U.S. Pat. No. 3,524,702, issued Aug. 18, 1970.
Although the apparatus disclosed in U.S. Pat. No. 3,524,702, is
practical and useful for the refracting of the eye, the apparatus
has certain disadvantages and deficiencies. For example, the
apparatus utilizes a single corrective refractive lens system
disposed between the patient's eye and the beam splitting element
along a portion of an optical path which is used for both the
incident and reflected rays with respect to the eye. In such
apparatus, optical interference in the form of reflections
frequently occurs within the lens element as both the incident and
reflected rays pass therethrough. In addition, the apparatus
utilizes a rotatable reticle and a rotatable disk light chopper.
The combination of reticle and light chopper is effective to
modulate the light beam and to provide a means for determining an
astigmatic condition, but the apparatus presents only one apparent
source of radiant energy to the patient's eye and requires a
relatively complex focus sensing mechanism in view of the rotation
of the image presented to the focus sensor.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide improved
apparatus for objectively testing and refracting the eye which
reduces stray light and optical interference between the light rays
incident to and reflected from the eye.
Another object of this invention is to provide apparatus for
refracting the eye which presents to the eye a moving slit image
representing two apparent sources of radiant energy at two distinct
effective distances.
Still another object of this invention is to provide apparatus for
objectively and automatically refracting the eye which provides for
the rotation of the light beam incident to the eye for the
determination of an astigmatic condition, while providing for a
relatively non-rotating reflected image for use in the analysis of
the reflected image.
Other and further objects and advantages of this invention will
become apparent from the following description when the same is
considered in connection with the accompanying drawings.
The apparatus in accordance with the present invention generally
utilizes the principles disclosed in U.S. Pat. No. 3,524,702, but
provides improved apparatus to more efficiently utilize those
principles. The apparatus of the present invention has the various
elements disposed along two optical paths to minimize stray light
and optical interference, commonly called "cross talk" often
occurring where beams of light are travelling in two directions,
essentially concurrently, through the same element. A source for
generating radiant energy is disposed along a first optical path
followed by modulating means aligned along that path. The
modulating means modulates a portion of the radiant energy
generated by the source therefor into a beam. Preferably, the
modulating means includes apparatus for modulating the portion of
radiant energy so as to present to the eye an image of a moving
slit representing in alternating succession two apparent sources of
radiant energy at two spaced apart distances. Such modulation can
be provided by two apertured and slotted discs rotating on a single
shaft as will be hereinafter described. The modulated light beam
travelling along the first optical path passes through a refractive
optical lens system which is used to determine the refractive
correction required by the eye. Thereafter, the beam of radiant
energy from the first optical path is directed into the patient's
eye for reflection from the retina of the eye. The reflected rays
pass from the eye and are directed along the second optical path,
for example, by means of a beam splitter, known to the art. The
reflected rays pass through a second optical lens system disposed
along the second optical path which is coupled to the first optical
lens system for varying the spatial relationship of the reflected
rays with the first optical lens system. The reflected rays from
the second optical lens system are directed along the second
optical path to analysis means which forms an image of the portion
of the beam of radiant energy reflected from the retina of the eye
and determines the sharpness of focus of that image. The analysis
means can comprise target means, such as an apertured reticle and a
focus sensor such as a suitable electro-optical sensor, for
example, a photo-multiplier tube. The target means serves to
dissect the image of the reflected rays at one or more apertures
thereof and the said image will be focused to approximately the
same degree as the light rays were in focus at the fundus on the
retina of the eye. The image at the target means will have lateral
motion imparted to the beam by the modulating means causing the
image to sweep over the target means resulting in light pulses
which are detected by the focus sensor. The focus sensor,
preferably, converts the pulses of light into an electrical signal
which itself is a measure of the degree of focus of the image
reflected by the fundus of the retina of the patient's eye. The
signal from the focus sensor is utilized to provide an indication
of the refractive correction required by the eye and may be
utilized to control the optical lens systems to achieve optimum
sharpness of focus of the instrument for the eye being
refracted.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing illustrating an embodiment of the
invention.
FIG. 2 is a perspective view of a double-blade modulating
arrangement.
FIG. 3 is a cross-sectional view of a variable power anamorphic
lens system.
FIG. 4 is an elevational view of a target.
FIG. 5 is a functional block diagram illustrating a system
embodying the invention.
FIG. 6 is a schematic diagram of an emmetropic eye (FIG. 6a), the
image therefrom as reflected and formed by the apparatus of this
invention (FIG. 6b) and the time varying electrical signal obtained
from said image in the apparatus of this invention (FIG. 6c).
FIG. 7 is a schematic diagram of a myopic eye prior to compensating
lens adjustment (FIG. 7a), the image therefrom as reflected and
formed by the apparatus of this invention (FIG. 7b) and the
electrical signal obtained from said image in the apparatus of this
invention (FIG. 7c).
FIG. 8 is a schematic diagram of a hypermetropic eye prior to
compensating lens adjustment (FIG. 8a), the image therefrom as
reflected and formed by the apparatus of this invention (FIG. 8b)
and the electrical signal obtained from said image in the apparatus
of this invention (FIG. 8c).
FIG. 9 is a functional block diagram illustrating in detail a
portion of the system shown in FIG. 5.
DESCRIPTION OF A PREFERRED EMBODIMENT
OPTICAL APPARATUS
In the construction shown in the drawings, with particular
reference to FIG. 1, the numeral 11 indicates a first optical path
and the numeral 12, a second optical path. The two optical paths
are distinct except for a short portion of a third optical path 13
along which rays of radiant energy travel from the first optical
path 11 toward the patient's eye 14 being tested and rays reflected
from the retina 16 of the patient's eye 14 travel toward second
optical path 12. While only a single optical system has been
illustrated and will be described, it will be understood that the
present invention contemplates the use of two such systems in a
single apparatus so that binocular refractive tests and other tests
may be made on the patient.
Arranged along first optical path 11 is a source for generating
radiant energy, such as an incandescent lamp 17, as shown. One or
more mirrors or lenses, or combinations thereof, (not shown) can be
used to concentrate and direct the rays of radiant energy from lamp
17 along first optical path 11, as known to the art. Lamp 17 may
provide continuous generation of radiant energy, for example,
illumination which is directed along first optical path 11.
Aligned with lamp 17 along first optical path 11 is a two-bladed
modulating arrangement indicated generally as 18 for modulating the
generated light rays into a beam. As more particularly shown in
FIG. 2, the modulating arrangement 18 includes a shaft 19 on which
two discs 21 and 22 are fixed for rotation therewith. Each disc 21,
22 contains a plurality of spaced radially aligned slots 23 and
apertures 24. The two discs are arranged on shaft 19 so that the
slots 23 of disc 21 are aligned with the center of apertures 24 of
disc 22 and, conversely, the slots 23 of disc 22 are aligned with
the apertures of disc 21. Thus, the rays of radiant energy from
lamp 17 along first optical path 11 are interrupted by the discs 21
and 22 to present to the eye 14 an image of a moving slit, that is,
of slots 23, representing in alternating succession two apparent
sources of radiant energy at two spaced apart distances. For
example, if an image of a slot 23 of disc 21 is presented along
first optical path 11, as shown in FIG. 2, the rays passing through
that slot also pass unimpeded through the aligned aperture 24 of
disc 22, the aperture serving to define the top and bottom of the
image of the slot. Therefore, the eye 14 perceives a slot image
apparently originating at disc 21. Upon rotation of the modulating
arrangement 18 about the axis of shaft 19 by a suitable motor (not
shown) the aperture 24 of disc 21 adjacent the aforementioned slot
of that disc enters alignment with first optical path 11, as does
the slot 23 of disc 22 adjacent the aforementioned aperture of that
disc. In such alignment, the rays generated by lamp 17 pass
unimpeded through the aperture of disc 21 until the slot of disc 22
is reached, the slot blocking all but a few of the rays. Thus, the
eye 14 perceives a slot image apparently originating at disc 22. An
additional aperture 25 masks the beam from the modulating
arrangement 18, so that only one slot image at a time is apparent
to the eye 14. Therefore, in alternate succession the eye 14 has
perceived an image of a moving slit from two apparent sources of
radiant energy at two spaced apart distances, the succession
continuing as long as generation and modulation of the rays are
maintained.
Next aligned along first optical path 11 with the modulating
arrangement 18 is a first image rotation prism 26 which serves to
project the moving slit image to the eye 14 at all possible angles
about the axis of optical paths 11 and 13 and to provide an
indication of astigmatism of the eye 14. Rotation of the image is
provided by mechanical rotation of prism 26 which must have an odd
number of internal reflections, such as a Pechan prism. Prism 26
can be rotated at a selected speed by a motor 28 (FIG. 5),
preferably, at a rotation rate above the critical flicker fusion
frequency, but below the frequency of the modulation imparted to
the image by modulating arrangement 18. In this range, the patient
does not perceive either the modulation or the rotation of the
image. In fact, the patient perceives only a patch of illumination
with fuzzy ill-defined edges absent of any visual cue for fixation
and accommodative tracking.
Further along first optical path 11 and aligned therewith is a
first lens system 29 for selectively varying the spatial
relationship of the rays of radiant energy from prism 26. As more
particularly shown in FIG. 3, lens system 29 may include a
spherical power focusing section 30 and a double cylinder section.
The spherical power focusing section 30 includes a
positive-negative three-element mechanically compensated zoom lens
comprising a fixed collimating lens 31, a movable positive zoom
lens element 32, and a fixed negative zoom lens element 33. The
double cylinder section comprises two cylindrical lenses, 34 and
36, which are independently rotatable about the axis of the lenses
which is coincident with the axis of first optical path 11. First
lens system 29 may comprise a lens system of these sections which
has independently variable spherical power, cylindrical power, and
cylinder axis orientation. The apparatus by which these sections
are controlled and the manner in which the information obtained by
such control is utilized will be hereinafter described in
conjunction with the description of FIG. 5. Other anamorphic zoom
lens designs with positive and negative powers can also be
utilized.
The rays of radiant energy generated by lamp 17 and which have been
modulated by modulating arrangement 18, rotated by prism 26 and
acted upon by lens system 29 are directed along first optical path
11 toward the patient's eye 14. As shown in FIG. 1, the rays from
lens system 29 are introduced into patient's eye 14 by means of
beam splitter 37. Beam splitter 37 serves to define one end of
first optical path 11 and to direct at least a portion of the beam
from that path along a short optical path 13 into the patient's eye
14. Optical path 13 is preferably short and does not contain any of
the optical elements of the apparatus to reduce the total amount of
stray light and optical interference entering the system as path 13
is also utilized for rays reflected from the patient's eye 14.
The beam of radiant energy moving along optical path 13 from beam
splitter 37 enters the patient's eye 14 with the slit image from
the two apparent distances being theoretically focused along
optical path 13 near or at a distance from the retina 16 depending
upon the refractive correction required by the eye 14. For example,
as shown in FIG. 6a with the apparatus calibrated for the
emmetropic eye, if eye 14 is an emmetropic eye, the slit image will
be close to focus with the point of focus A for the image of slots
23 of disc 21 being just in front of the retina 16 of the eye 14
and the point of focus B for the image of slots 23 of disc 22 being
just behind the retina 16. A myopic eye will focus the image
forwardly of these points in relation to the retina as in FIG. 7a,
while a hypermetropic eye will focus rearwardly of these points in
relation to the retina 16, as in FIG. 8a.
A portion of the radiant energy incident to the eye is reflected by
the retina 16 back through the lens 38 of the eye 14 along optical
path 13 toward beam splitter 37. The sharpness of focus of the
image is directly related to the refractive condition of the eye
14, that is, the distance of the center between the two points of
focus of the image A and B, from the retina, as shown in FIGS. 6a,
7a, and 8a. Thus, for the emmetropic eye the distances between A
and the retina 16, and B and the retina 16 are approximately equal,
(FIG. 6a) and the focus of the two images will be equally sharp.
Beam splitter 37 receives the portion of the beam of incident rays
reflected from the retina 16 and projects at least a portion
thereof along second optical path 12.
Aligned along second optical path 12 is a second lens system 39 and
a second image rotation prism 41. Second lens system 39 can be
identical to first lens system 29, for example with an identical
spherical power focusing section 42 and an identical double
cylinder section having cylindrical lenses 43 and 44. Second lens
system 39 can be coupled to first lens system 29 for varying the
spatial relationship of the reflected portion of the beam moving
along second optical path 12 with and to the same extent as the
beam moving along first optical path 11 is varied by first lens
system 29. Similarly, prism 41 can be identical to prism 26 and can
be coupled thereto to rotate prism 41 at the same speed. Prism 41
serves to "derotate" the image in the reflected beam, i.e., to
remove the apparent rotation of the image imparted by first prism
26.
A target, such as an apertured reticle 46 is aligned along second
optical path 12 at which the reflected beam forms an image which is
focused to approximately the same degree as the light rays were in
focus at the fundus of the retina 16 of eye 14, for example, as
shown in FIGS. 6b, 7b and 8b. Reticle 46, preferably, has a
plurality of radial slot apertures 47, as shown in FIG. 4, radially
aligned with the slots of the discs 21 and 22. Alternatively, a
reticle with a single slot aperture (not shown) can be used.
Optical path 12 is terminated at a radiant energy sensor, such as
photo-multiplier tube 48. Tube 48 detects light pulses passing
through apertures 47 of reticle 46 and converts the light pulses
into an electrical signal which correspond to the degree of focus
of the image reflected by the fundus of the retina 16 of eye 14.
FIGS. 6c, 7c and 8c are illustrative of the electrical signal
obtained for the emmetropic, myopic and hypermetropic eyes shown in
FIGS. 6a, 7a and 8a, respectively. The utilization of the
electrical signal in the present invention will be hereinafter
described. Optical path 12 is shown in FIG. 1 as being folded
through the use of a mirror 49. However it is understood that
optical path 12 may be a straight path, thus eliminating the need
for mirror 49. By using a folding or movable mirror for mirror 49,
and moving the mirror out of the second optical path 12, the
apparatus can be utilized for visual examination of retina 16 by an
operator 51 through an eye piece lens 53.
In addition, the apparatus can be used to subjectively test the
refractive correction of the eye 14, for example, to confirm a
correction previously indicated objectively by the apparatus, by
inserting a mirror (not shown) and one or more back-illuminated
visual acuity or other charts (not shown) into the first optical
path 11, or second optical path 12, as described in U.S. Pat. No.
3,524,702. The optical magnification of the apparatus is such that
the charts may be of microfilm dimensions resulting in a compact
machine wherein even the use of charts may be readily
automated.
MECHANICAL APPARATUS
Referring particularly to FIG. 5, the apparatus of this embodiment
of the present invention utilizes motor 28 to rotate prisms 26 and
41 synchronously; a motor 54, such as a servo motor, to control the
spherical power focusing sections 30 and 42 of lens systems 29 and
39, respectively; and a pair of motors 56 and 57, such as a pair of
servo motors, to synchronously control the first cylindrical
elements 34 and 43 of each of lens systems 29 and 39, and the
second cylindrical elements 36 and 44 of each of lens systems 29
and 39, respectively. The shafts (not shown) of these motors can be
connected by suitable gear systems to mechanisms supporting the
corresponding lens elements as is known to the art. The motors 54,
56 and 57 have the capability of rotating their output shafts in
either of two directions and are controlled by electronic motor
controllers as will be hereinafter described.
ELECTRONIC APPARATUS
As stated above, the optical elements of the apparatus are
controlled by the electronic components of the apparatus, and the
correction required by the eye 14 is determined and indicated by
these electronic components. In operation of the apparatus, the
lamp 17 is energized and the eye 14 to be tested is brought into
position in alignment with optical path 13 at a predetermined
distance from beam splitter 37. Modulating arrangement 18 is
rotated at a constant speed as heretofore described and motor 28 is
energized to rotate prisms 26 and 41 at a predetermined speed.
Under these conditions an image in the form of light pulses sweeps
past the aperture 47 of reticle 46, as in FIGS. 6b, 7b or 8b, and
photomultiplier tube 48 converts the light pulses to an electrical
signal whose characteristics are a measure of the degree of focus
of the instrument including the patient's eye 14, as shown in FIGS.
6c, 7c or 8c.
Referring to FIG. 5, the electrical signal from photomultiplier
tube 48 is amplified by an amplifier 58 and filtered through a low
frequency filter 59. The amplified and filtered signal contains the
information from the image of both apparent radiant energy sources
resulting from the action of the modulating arrangement 18. The
separation of the two components of the signal is effected through
the creation of a reference signal.
As more particularly shown in FIG. 2, a small lamp 61 is mounted
between discs 21 and 22 aligned with the slots 23 and apertures 24
of the discs, or reference slits (not shown), so that light from
lamp 61 is aligned with a slot 23 radially outside of aperature 24
of each disc whenever another slot of that disc is aligned with
lamp 17 along optical path 11. The slots 23 extend to the edge of
the discs 21 and 22, whereas the apertures 24 do not. A pair of
photodiodes 62 aligned with lamp 61 on the opposite side of each of
discs 21 and 22, provides a reference signal indicative of which
disc is providing the slot 23 which is the apparent source of the
image appearing at reticle 46 at a particular instant.
Alternatively, a single photodiode can be used in place of the pair
of photodiodes 62, by using suitable electronic timing circuits or
by widening the slots 23 equal to the spacing between the slots and
utilizing a "flip-flop" switch circuit to indicate which disc is
the apparent source of the slot image at any instant.
The reference signal from photodiodes 62 is used to operate two
analog switches 63 and 64 by passing the signal through two gating
circuits 65 and 66. It is assumed for the purpose of this
description that the circuits and switches are connected so that
the portion of the signal resulting from the use of the slots 23 of
disc 21 correspond with channel A and that the portion of the
signal resulting from the use of the slots 23 of disc 22 correspond
with channel B. As shown in FIG. 5, the electrical signal from
filter 59 is fed to both switches 63 and 64 which separates the
signal into two signals, A and B, respectively, corresponding to
whichever switch is made operative by the gating circuits 65, 66.
Signals A and B are amplified and filtered through amplfiers 67 and
68 and filters 69 and 71, and then compared in a differential
amplifier 72 which generates a signal which is proportional to the
difference between the two input signal, A and B, and provides an
indication of the direction and magnitude of correction required to
achieve optimum sharpness of focus. The signal from the
differential amplifier 72 is fed to an electronic motor control
circuit 73 where the signal is utilized to energize motor 54 to
control spherical power focusing sections 30 and 42 of the lens
systems 29 and 39, respectively. In this manner the lens systems
are adjusted for spherical power so as to achieve optimum sharpness
of focus for the apparatus including the patient's eye 14. Upon the
spherical power focusing sections 30 and 42 of the lens systems
reaching adjustment for optimum sharpness of focus, the electrical
signals A and B will be equal, similar to the signal shown in FIG.
6c, and differential amplifier will cease to generate a
differential signal, a null condition having been attained. The
movement required by the spherical power focusing sections in
attaining the desired condition is indicated on position sensing
apparatus 74, such as a meter or gauge.
In a similar manner, correction is made for an astigmatic
condition. The presence of astigmatism in the image at reticle 46
will result in the electrical signal fluctuating at the frequency
of the image rotation induced by the rotating prism 26. The
magnitude of the fluctuation at the image rotation frequency is a
measure of the magnitude of the astigmatism and the time
relationship of the signal to a reference signal will indicate the
location of the astigmatic axis. In particular, the amplified and
filtered electrical signal from filter 59 is fed to an amplfier 76
for further amplification, as well as to analog switches 63 and 64
as described above. The further amplified signal from amplifer 76
is passed through a bandpass filter 77 which is tuned to the image
rotation frequency.
The reference signal for astigmatism is obtained by a reference
signal generator 78 coupled to the image rotation prisms 26 and 41
and the motor 28, the signal being amplified by amplifier 79, acted
upon by squaring circuit 81. A comparison of the time phase of this
reference signal with the phase of the signal from filter 77, which
represents the magnitude of the astigmatism, is made by analog
switch 83. The resulting signal (phase signal) indicates the
astigmatism angle and is further filtered by filter 84 and
amplified by amplfier 86. The signal from filter 77 is also
amplified, by amplifier 87, and both signals are fed to motor
control circuit 88 which controls motors 56 and 57 coupled to
cylindrical power and axis elements 34, 36, 43, and 44. These
cylindrical elements will be rotated by the motors to the proper
net angle of each element to its adjacent element to match the
astigmatic axis of the eye 14 and then counter-rotated until the
astigmatism magnitude signal is reduced below a threshold value. At
this point the lens systems 29 and 39 contain the corrective
prescription of the patient's eye and position sensor 74 as well as
similar position sensors 89 and 91, all of which are controlled by
an analog computer 90, will display the prescription as hereinafter
described.
The conversion of the lens element position data into conventional
eye class prescription information requires some minor computation
and may be accomplished with an analog computer 90 as shown in FIG.
9. The total spherical power is the sum of the spherical power
indicated by a position sensor 94, which senses the position of
spherical power focusing section 30 or 42 (only section 42 being
shown in the drawing), and a contribution due to the cylindrical
(crossed) lenses 43 and 44 (lenses 34 and 36 alternatively may be
used). Position sensor 94 can be a linear potentiometer coupled to
the spherical power focusing section 42 and/or section 30 or the
motor 54, desirably, for example, having a value of approximately
100 megohms. A differential gear coupling 93 coupled to cylindrical
lenses 43 and 44, or their motors 56 and 57, respectively,
indicates the relative angle between the two cylinder axes thereof
independent of their absolute rotational positions. The
contribution to the total spherical power due to the cylindrical
elements 43 and 44 is measured by 1-cosine of the angle (angle
.phi.) between their two cylinder axes and is sensed by a special
function (1-cosine .phi.) potentiometer 98 attached to the output
of the differential gear coupling 93. Potentiometer 98, for
example, can have a value of approximately 20 megohms. The total
spherical power is displayed on position sensor 74, which may be a
meter or indicator calibrated in accordance with potentiometers 94
and 98. The net cylindrical power of the cylindrical lens
combination is determined by the cosine of the said relative angle
(cosine .phi.) and is sensed by potentiometer 97 and displayed by a
position sensor 89, such as a meter calibrated thereto.
Potentiometer 97, for example, can have a value of approximately
100 megohms. The composite cylinder angle is determined by the
absolute rotational position of one of the cylindrical lenses 43
and 44, such as 43 as shown, used as a reference, and is sensed by
a linear potentiometer 95. Potentiometer 95, for example, can have
a value of approvimately 180 megohms with a calibrated range of one
megohm per degree of angular rotation. The signal from
potentiometer 95 is added to half the rotational angle (angle
.phi.) between the cylindrical lenses 43 and 44, sensed by
potentiometer 96 and the resulting value displayed by meter 91
calibrated thereto. Potentiometer 96, for example, can have a value
of approximately 45 megohms with a range of 0.5 megohm per degree
of angular rotation.
It is understood that this computation may be provided by other
means, such as a correction in the optics, by digital computer or
other means, as well as the analog computer described above.
Various changes coming within the spirit of our invention may
suggest themselves to those skilled in the art; hence we do not
wish to be limited to the specific embodiment shown and described
or uses mentioned, but intend the same to be merely exemplary, the
scope of our invention being limited only by the appended
claims.
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